Communication device and communication method for determining a combination of base stations used to communicate with a communication terminal

ABSTRACT

An electronic device that communicates with a plurality of base stations by Coordinated Multiple Point transmission and reception (CoMP), the base stations including at least a first base station and a second base station. The electronic device receives configuration information from the first base station, the configuration information indicating a first period of a first reference resource; and receives a second reference resource from the second base station during the first period. The first reference resource corresponds to a muted power Channel State Information-Reference Signal (CSI-RS) and the second reference resource corresponds to a non-muted power CSI-RS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 14/123,654 filed Dec. 3, 2013, which is the U.S. National Stageapplication of PCT International Application No. PCT/JP2012/004066 filedJun. 22, 2012, which claims priority to Japanese Application No.2011-150550 filed Jul. 7, 2011. U.S. application Ser. No. 14/123,654 isherein incorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates to a communication device, and acommunication method.

BACKGROUND ART

Recently, a cellular system of fourth generation (4G) is discussed toachieve further improvements on the performance of wirelesscommunication. In the 4G, relay technology, carrier aggregation, andCoordinated Multiple Point transmission and reception (CoMP) technologyare paid attention.

The relay technology is a technology by which a relay node relayscommunication between a base station (for instance, a macrocell basestation) and a communication terminal, and is important in improvingcell-edge throughput of the base station. Moreover, the carrieraggregation is a technology that extends a usage bandwidth (forinstance, 20 MHz*5=100 MHz) and achieves an improvement in maximumthroughput by collectively treating a plurality of frequency bands thathave a bandwidth of 20 MHz. Moreover, the CoMP is a technology by whicha plurality of base stations called a CoMP set cooperates to communicatedata with a communication terminal, and can expand the coverage that cansupport communication at high data rates. The CoMP is disclosed inPatent Document 1, for example.

Moreover, in the 4G, it is being discussed to improve the coverage byintroducing base stations other than macro-eNodeBs, for example, byintroducing Home eNodeBs (femtocell base stations, micro-base stationsfor mobile phones), remote radio heads (RRHs), and pico-eNodeBs.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Application Laid-Open No. 2011-091785

SUMMARY Technical Problem

In this way, in a heterogeneous environment in which various kinds ofbase stations such as RRHs, macro eNodeBs, and the like are dispersed,it is anticipated that even the CoMP set might dynamically change.However, methods of determining the CoMP set in the heterogeneousenvironment are not sufficiently discussed.

Accordingly, the present disclosure proposes a novel and improvedcommunication device, communication method, program, and communicationsystem for appropriately determining a combination of base stations usedto communicate with a communication terminal.

Solution to Problem

According to the present disclosure, provided is a communication deviceincluding a receiver that receives information indicating timing atwhich a predetermined signal is transmitted a transmitting base stationof a plurality of base stations having the same cell ID. The receiverdetermines that the predetermined signal has been transmitted from thetransmitting base station based on the timing observed by the receiver

Moreover, according to the present disclosure, further provided is acommunication method that includes receiving wirelessly at a userequipment receiver information indicating a timing at which apredetermined signal is transmitted from a transmitting base station ofa plurality of base stations having a same cell ID; and determining thatthe predetermined signal has been transmitted from the transmitting basestation based on the timing observed by said user equipment receiver.

Moreover, according to the present disclosure, yet further provided is acommunication a communication controlling device and method that uses asetting unit that sets a timing at which a predetermined signal istransmitted only from some base stations of a plurality of base stationshaving a same cell ID so a user equipment can determine that thepredetermined signal has been transmitted from a transmitting basestation based on a receive timing observed by the user equipment.

Advantageous Effects of Invention

According to the present disclosure as described above, it is possibleto appropriately determine a combination of base stations used tocommunicate with a communication terminal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram illustrating a configuration of acommunication system according to an embodiment of the presentdisclosure.

FIG. 2 is an explanatory diagram illustrating a frame format of 4G.

FIG. 3 is an explanatory diagram illustrating an example of anembodiment of CoMP.

FIG. 4 is an explanatory diagram illustrating another example of theembodiment of the CoMP.

FIG. 5 is a functional block diagram illustrating configurations of aneNodeB and an RRH according to a first embodiment.

FIG. 6 is an explanatory diagram illustrating a subframe which is set asan ABS.

FIG. 7 is an explanatory diagram illustrating subframes which are set asan ABS and a Multimedia Broadcast multicast Single Frequency Network(MBSFN).

FIG. 8 is an explanatory diagram illustrating an example of setting anABS.

FIG. 9 is an explanatory diagram illustrating another example of settingan ABS.

FIG. 10 is an explanatory diagram illustrating an example of setting anABS when base stations are grouped.

FIG. 11 is an explanatory diagram illustrating an example of informationthat is held by an RSRP holding unit.

FIG. 12 is a functional block diagram illustrating a configuration of aUE according to the first embodiment.

FIG. 13 is a flowchart illustrating an operation of a communicationsystem.

FIG. 14 is an explanatory diagram illustrating a modification of amethod of setting an ABS.

FIG. 15 is a functional block diagram illustrating configurations of aneNodeB and an RRH according to a second embodiment of the presentdisclosure.

FIG. 16 is an explanatory diagram illustrating a specific example of aCSI-RS insertion period.

FIG. 17 is an explanatory diagram illustrating an example of setting theCSI-RS insertion period when RRHs are grouped.

FIG. 18 is a functional block diagram illustrating a configuration of aUE according to the second embodiment.

FIG. 19 is a flowchart illustrating an operation of a communicationsystem.

FIG. 20 is an explanatory diagram illustrating a modification of theCSI-RS insertion period.

FIG. 21 is an explanatory diagram illustrating CSI-RS+Enhanced_Mutingaccording to the second modification.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present disclosure are described below indetail referring to the accompanying drawings. Throughout the presentspecification and drawings, components having substantially the samefunctional configuration are denoted by the same reference letters ornumbers and thus a redundant description about such components will notbe made.

Moreover, a plurality of components having substantially the samefunctional configuration may be distinguished sometimes by differentalphabets added to the last part of the same reference letters in thisspecification and the drawings. For instance, a plurality of componentshaving substantially the same functional configuration may bedistinguished like RRHs 30A, 30B, and 30C if necessary. However, when aplurality of components having substantially the same functionalconfiguration need not necessarily be distinguished from each other,such components may be denoted only by the same reference letter. Forinstance, when RRHs 30A, 30B, and 30C need not be necessarilydistinguished from each other, they are only referred to as RRHs 30.

Moreover, the present disclosure is described in the following order ofitems.

1. Overall configuration of communication system

2. First embodiment

2-1. Configuration of base station

2-2. Configuration of UE

2-3. Operation of communication system

2-4. Modification

3. Second embodiment

3-1. Regarding CSI-RS

3-2. Configuration of base station

3-3. Configuration of UE

3-4. Operation of communication system

3-5. First modification

3-6. Second modification

4. Conclusion

<1. Overall Configuration of Communication System>

The technology according to the present disclosure may be executed invarious modes as described in detail, for example, in sections from “2.First embodiment” to “3. Second embodiment”. Moreover, a communicationdevice (UE 20) according to each of embodiments includes:

A. a receiver (antenna group 204 and the like) that receives informationthat indicates timing at which a specific signal is transmitted onlyfrom some base stations of a plurality of base stations having the samecell ID;

B. a measuring unit (DL signal detector 230) that measures receptionpower at the timing; and

C. a transmitter (antenna group 204 and the like) that transmits themeasurement result obtained by the measuring unit.

Hereinbelow, basic components that are common in respective embodimentsare described first by referring to FIGS. 1 and 2.

(Overall Configuration of Communication System)

FIG. 1 is an explanatory diagram illustrating a configuration of acommunication system 1 according to an embodiment of the presentdisclosure. As illustrated in FIG. 1, the communication system 1according to the embodiment of the present disclosure includes an eNodeB10, a core network 12, a user equipment (UE) 20, and a plurality of RRHs30A to 30F.

The UE 20 is a communication device that performs reception processingfor a down-link resource block that is allocated by a base station suchas the eNodeB 10, and performs transmission processing for an up-linkresource block.

The UE 20 may be a smart phone shown in FIG. 1 for instance, or may bean information processing device such as a personal computer (PC), ahome-use video processing device (DVD recorder, VCR, and the like), apersonal digital assistants (PDA), a family-use game console, or a homeelectric appliance. In addition, the UE 20 may be a mobile communicationdevice such as a mobile phone, a personal handyphone system (PHS), aportable music player, a portable video processing device, or a portablegame console.

The eNodeB 10 is a radio base station that communicates with the UE 20in the coverage (in this specification, the eNodeB 10 indicates aMacro_eNodeB unless specifically described otherwise). Moreover, theeNodeB 10 is connected to a plurality of RRHs 30A to 30F through acommunication path such as an optical fiber for instance. Therefore, theeNodeB 10 can transmit a down-link signal to the RRH 30 through thecommunication path and cause the RRH 30 to transmit the down-link signalto the UE 20, or can receive an up-link signal, which the RRH 30 hasreceived from the UE 20, from the RRH 30. In addition, it is alsopossible for the eNodeB 10 to perform CoMP communication by cooperatingwith the plurality of RRHs 30A to 30F. Details of the CoMP communicationwill be described later. Although not illustrated in FIG. 1, a lot ofthe eNodeBs 10 are actually connected to a core network 12.

The core network is a service-provider's network including managementnodes such as a mobility management entity (MME) and a serving gateway(GW). The MME is a device that sets a session for data communication,and controls opening and hand-over. This MME is connected to the eNodeB10 through an interface called X2. The S-GW is a device that routes andforwards user data.

The RRH 30 is a radio base station which communicates with the UE 20with relatively small power compared with the eNodeB 10. Specifically,the RRH 30 is connected to the eNodeB 10 through a communication pathsuch as an optical fiber and transmits the down-link signal, which hasbeen received from the eNodeB 10 through this communication path, to theUE 20. Moreover, the RRH 30 transmits the up-link signal, which has beenreceived from the UE 20, to the eNodeB 10 through the communicationpath. The communication system 1 according to the present disclosureincludes the RRHs 30 so that the coverage and the quality in thevicinity of the cell edge can be improved.

(Frame Configuration)

Next, a radio frame shared between the UE 20 and a base station such asthe eNodeB 10 is described.

FIG. 2 is an explanatory diagram illustrating a frame format of 4G. Asillustrated in FIG. 2, a radio frame of 10 ms includes ten subframes #0to #9 each of which is 1 ms. Each subframe is one resource blockincluding twelve subcarriers/fourteen orthogonal frequency divisionmultiplexing (OFDM) symbols, and scheduling is assigned in units of aresource block. Moreover, a single OFDM symbol corresponds to a unitused in a communication system of an OFDM modulation system, and is theunit for outputting data which is processed through one time of fastFourier transform (FFT).

Moreover, as illustrated in FIG. 2, each subframe includes a controlregion and a data region. The control region includes first one to threeOFDM symbols (FIG. 2 shows an example in which the control regionincludes three OFDM symbols) and is used to transmit a control signalthat is called phy downLink control channel (PDCCH). Further, the dataregion following the control region is used to transmit user data or thelike that is called phy downLink shared channel (PDSCH).

In addition, a cell-specific common reference signal (CRS) that is acell-specific reference signal is disposed in the control region and thedata region. The UE 20 performs channel estimation by receiving thisCRS, and can demodulate the PDSCH and the like on the basis of thechannel estimation result.

(Regarding CoMP)

Next, the CoMP that relates to the present disclosure is described. TheCoMP is a technology by which a plurality of base stations called a CoMPset cooperates to communicate data with the UE 20, and can extend thecoverage which can support communication at high data rates. This CoMPis divided roughly into Joint Processing and Coordinated Schedulingand/or Beamforming.

The former, Joint Processing, is a technology by which a plurality ofbase stations communicates data with one UE 20 at the same time. Forinstance, as illustrated in FIG. 3, an example in which the eNodeB 10and the RRHs 30A to 30F transmit data to the UE 20 at the same timecomes under the Joint Processing. According to this Joint Processing,since branches (antennas and analog circuits (wireless processingunits)) of a plurality of base stations can be used for datacommunication, the antenna gain and SINR can be improved.

When Joint Processing for down-link is performed, transmission data tothe UE 20 should be distributed to the RRHs 30A to 30F through a wiredcommunication path, for example, called a backing hole between the basestations beforehand. Moreover, the Joint Processing for up-link isperformed by integrating the data received by a plurality of basestations from the UE 20.

Examples of the data integration method include a method of integratingdata of a bit level which has been demodulated by each of the basestations, a method of integrating data of a soft bit level which has notyet been decoded by each of the base stations, a method of integratingdata which has not yet been demapped by each of the base stations, andthe like. As the data is integrated after latter part of the data isdemodulated in each base station, the amount of data which is exchangedthrough the backing hall increases, but the performance tends toimprove.

The latter, the Coordinated Scheduling and/or Beamforming, is atechnology by which data transmission is performed only by one basestation and scheduling (control that determines resource blocks to beallocated to respective UEs 20) is performed cooperatively by theplurality of base stations. According to this Coordinated Schedulingand/or Beamforming, interference among the plurality of base stationscan be easily avoided by performing scheduling adjustment.

The technology according to the present disclosure especially focuses onthe former, that is, Joint Processing, among the two kinds of CoMPs.This Joint Processing is roughly classified into Non-Coherent JointProcessing and Coherent Joint Processing.

The Coherent Joint Processing is an adjustment method of adjustingtiming of data transmission from each of the base stations so thatphases of data, which arrives at a communication terminal 20 from therespective base stations, match. On the other hand, the Non-CoherentJoint Processing is a method in which each of the base stationstransmits data without adjusting timing of data transmission from eachof the base stations. Therefore, the Coherent Joint Processing issuperior in performance to the Non-Coherent Joint Processing. However,in order to perform the Coherent Joint Processing, it is necessary tocalculate an adjustment amount of transmission timing of each of thebase stations 10 for every communication terminal 20. Accordingly, it isdisadvantageous in terms of complex processing.

(Regarding CoMP Set)

The CoMP set is a term used in 3GPP, and it means a combination of basestations which cooperatively perform transmission for the purpose ofperforming the CoMP. Usually, it is assumed that about three eNodeBs 10compose the CoMP set. On the other hand, three or more base stations,such as five or ten, compose the CoMP set in an heterogeneousenvironment in which cells such as Pico_eNodeBs, Home_eNodeBs, RRHeNodeBs (in this specification, simply called RRHs), and the like areoverlaid. Moreover, it is anticipated that the CoMP set dynamicallychanges.

By the way, since the distances to the respective base stations aredifferent depending on the UEs 20, the best CoMP set is different foreach of the UEs 20. Therefore, it is important to determine the bestCoMP set for each of the UEs 20. For instance, the CoMP set can bedetermined in such a manner that the base stations receive the reportsof reference signal received power (RSRP) of CRS that each of the UEs 20has acquired in a frame-synchronized manner with each of the basestations and the base stations where the RSRP is large are selected fromamong the plurality of base stations that are reported from the UEs 20.

(Relation Between Cell ID and CoMP)

The above-mentioned Macro_eNodeBs 10 usually have cell IDs which aredifferent for each of the Macro_eNodeBs 10. Similarly, it has beenassumed for the RRHs 30 to have cell IDs different for each of the RRHs30. However, recently, a scenario is being discussed in which theplurality of RRHs 30 that belongs to a certain Macro eNodeB 10 sharesthe same cell ID with the Macro_eNodeB 10. In this case, since theMacro_eNodeB 10 and the plurality of RRHs 30 transmit the same signal,there are advantages that an intercell interference of the RRHs 30 doesnot occur and it is easy to execute the CoMP while there is also adisadvantage that the cell gain is not improved.

(Point Aimed by This Embodiment)

Since the cell ID and the reference signal like the CRS are inone-to-one correspondence when the eNodeB 10 and all of the RRHs 30 havethe same cell ID as described above, it is considered that the CRSs thatare transmitted by the eNodeB 10 and each of the RRHs 30 are identical.Therefore, even if the UE 20 attempts to measure and report the RSSP ofthe CRS transmitted from each of the RRHs 30, it is difficult todistinguish the sending station of the CRS. Therefore, it is alsodifficult for the eNodeB 10 to select the best CoMP set for the UE 20.As a result, as illustrated in FIG. 3, a method is considered in whichthe eNodeB 10 and all of the RRHs 30 perform the CoMP with respect tothe UE 20.

FIG. 3 is an explanatory diagram illustrating an example of theembodiment of the CoMP. When the eNodeB 10 and all of the RRHs 30perform the CoMP with respect to the UE 20 as illustrated in FIG. 3, theUE 20 improves the reception quality by receiving the same signal fromthe eNodeB 10 and all of the RRHs 30.

However, when it is discussed in detail, the signal transmissions fromthe RRHs 30D and 30E do not really contribute to the improvement of thereception quality of the UE 20 because the reception power from the RRHs30D and 30E that are far from the UE 20 is low. The signal transmissionsfrom the RRHs 30D and 30E act as an interference wave and thus isconsidered to cause degradation of the throughput of the entire system.

Therefore, ideally as illustrated in FIG. 4, it is preferable that theCoMP be performed by using only a part of the RRHs 30 (for instance,RRHs 30A and 30B) that contribute to the improvement of the receptionquality of the UE 20. However, there was no means to select the bestCoMP set for the UE 20 as described above. In this respect, since theconventional UEs of Re18, Re19, and Rel10 expect the same signal to betransmitted from each of the RRHs, if the respective RRHs 30 transmitsignals by which the respective RRHs can be distinguished while therespective RRHs 30 have the same cell ID, the compatibility may be lost.

Therefore, in view of the above-mentioned circumstances, each embodimentof the present disclosure has been made. According to each embodiment ofthe present disclosure, the best CoMP set for the UE 20 can bedetermined by obtaining the RSRP of each of the RRHs 30 in the UE 20.Hereinbelow, each embodiment of the present disclosure is described indetail as follows.

<2. First Embodiment>

(2-1. Configuration of Base Station)

FIG. 5 is a functional block diagram illustrating configurations of aneNodeB 10-1 and RRHs 30 according to a first embodiment. As illustratedin FIG. 5, each of the RRHs 30 includes an antenna group 304 and awireless processing unit 310, and transmits a down-link signal, suppliedby the eNodeB 10-1 through an optical fiber, to a UE 20-1 according tothe first embodiment. Moreover, each of the RRHs 30 supplies an up-linksignal received from the UE 20-1 to the eNodeB 10-1 through the opticalfiber. Each of the RRHs 30 has the same cell ID as the eNodeB 10-1, andtransmits the same cell-specific reference signal (for instance, CRS).

Moreover, as illustrated in FIG. 5, the eNodeB 10-1 includes an antennagroup 104, a wireless processing unit 110, a DA/AD converter 120, anup-link (UL) signal detector 130, a scheduler 140, a down-link (DL)signal generator 150, an ABS setting holding unit 160, an RSRP holdingunit 170, and a CoMP set determining unit 180. Almost blank subframe(ABS) is a technology that is decided to be adopted in Rel10 of 3GPP,and the ABS is a subframe most of which is stopped from beingtransmitted. For instance, only PDCCH and CRS are transmitted in asubframe which is set as the ABS. The first embodiment is made by payingattention to the ABS.

The antenna group 104 receives a radio signal from the UE 20-1, acquiresan electric high frequency signal, and supplies the high frequencysignal to the wireless processing unit 110. Moreover, the antenna group104 transmits the radio signal to the UE 20-1 on the basis of the highfrequency signal supplied from the wireless processing unit 110. Sincethe eNodeB 10-1 includes the antenna group 104 including a plurality ofantennas, the eNodeB 10-1 can perform MIMO communication and diversitycommunication.

The wireless processing unit 110 converts a high frequency signalsupplied by the antenna group 104 to a baseband signal (up-link signal)by performing analog processing such as amplification, filtering, ordown conversion. Moreover, the wireless processing unit 110 converts thebaseband signal (down-link signal) supplied by the DA/AD converter 120into the high frequency signal.

The DA/AD converter 120 converts the up-link signal of an analog formatsupplied from the wireless processing unit 110 into a digital format,and supplies the converted signal to the UL signal detector 130.Moreover, the DA/AD converter 120 converts the down-link signal of thedigital format supplied from the DL signal generator 150 into the analogformat, and supplies the converted signal to the wireless processingunit 110.

Moreover, the down-link signals for the respective RRHs 30 are suppliedto the DA/AD converter 120 from the DL signal generator 150. Therefore,the DA/AD converter 120 converts the down-link signal for each of theseRRHs 30 into the analog format, and supplies the converted signal to thecorresponding RRH 30 through the optical fiber. The DA/AD converter 120is supplied with the up-link signal from each of the RRHs 30 through theoptical fiber, converts the up-link signal into the digital format, andsupplies the converted signal to the UL signal detector 130.

The UL signal detector 130 detects a control signal such as PUCCH oruser data such as PUSCH from the up-link signal supplied by the DA/ADconverter 120. In particular, the UL signal detector 130 according tothis embodiment detects an RSRP measurement result obtained through CRSmeasurement in the UE 20-1 from the up-link signal supplied by the DA/ADconverter 120. The RSRP measurement result may be included in the PUSCH.

The scheduler 140 schedules resources to be used by the eNodeB 10-1,each of the RRHs 30, and the UE 20-1 for communication. In particular,the scheduler 140 according to this embodiment performs scheduling onthe basis of the base station (the eNodeB 10-1 or each of the RRHs 30)where the ABS is set by the ABS setting holding unit 160 and a positionof the subframe. Moreover, the scheduler 140 schedules the communicationwith the UE 20-1 by using the CoMP set for the UE 20-1 which isdetermined by the CoMP set determining unit 180.

The DL signal generator 150 generates the down-link signal to betransmitted from the eNodeB 10-1 and each of the RRHs 30. Specifically,the DL signal generator 150 generates PDCCH, PDSCH, and the likeaccording to the scheduling by the scheduler 140. In addition, the DLsignal generator 150 according to this embodiment sets the position ofthe subframe, which is specified by the ABS setting holding unit 160 asthe ABS, in the ABS for the eNodeB 10-1 and each of the RRHs 30.Moreover, the PDCCH or PDSCH may contain information on the ABS which isset by the ABS setting holding unit 160. Hereinbelow, the subframe whichis set as the ABS is described in detail referring to FIGS. 6 and 7.

FIG. 6 is an explanatory diagram illustrating a subframe which is set asan ABS. In the subframe which is set as the ABS as illustrated in FIG.6, the PDSCH is not transmitted in a data region. On the other hand,transmission of the PDCCH and the CRS (reference signal) is not stoppedin the data region.

FIG. 7 is an explanatory diagram illustrating a subframe which is set asboth an ABS and a multimedia broadcast multicast single frequencynetwork (MBSFN). As illustrated in FIG. 7, all transmissions except atransmission of a CRS can be stopped in the control region by settingboth the ABS and the MBSFN to the subframe. In this embodiment, asdescribed in detail later, the ABS and the MBSFN are set in the eNodeB10-1 and each of the RRHs 30 so that the RSRPs of the respective RRHs 30can be obtained in the UE 20-1.

Here, returning to the description about the configuration of the eNodeB10-1 with reference to FIG. 5, the ABS setting holding unit 160 sets theABS (which may contain the MBSFN, the same hereinbelow) with respect toat least part of subframes of the eNodeB 10-1 and the RRHs 30A to 30F.The ABS setting holding unit 160 associates and holds information thatindicates the subframe set as the ABS and information that indicates thebase station where the ABS is set.

The ABS setting holding unit 160 sets the same subframe as the ABS inthe base stations except one base station, or except two or more basestations among the eNodeB 10-1 and the RRHs 30A to 30F. As a result, inthe subframes that are set as the ABS, only one base station or only twoor more base stations will transmit a CRS in the data region. Hereafter,setting of such an ABS is described more specifically referring to FIGS.8 to 10.

FIG. 8 is an explanatory diagram illustrating an example of setting theABS. When a subframe #3 of radio frames #M to #N is set as the ABS inthe eNodeB 10-1 and the RRHs 30B to 30F excluding the RRH 30A asillustrated in the first row of FIG. 8, only the RRH 30A transmits theCRS in the data region of the subframe #3 of the radio frames #M to #Nas illustrated in the upper part of FIG. 9.

Similarly, when the subframe #3 of the radio frames #N+1 to #O is set asthe ABS in the eNodeB 10-1, the RRH 30A, and the RRHs 30C to 30Fexcluding the RRH 30B as illustrated in the second row of FIG. 8, onlythe RRH 30B transmits the CRS in the data region of the subframe #3 ofthe radio frames #N+1 to #O as illustrated in the lower part of FIG. 9.By repeating such a setting, it is possible to generate the subframeswith the data region in which only each of the RRHs 30A to 30F cantransmit the CRS.

Although the example of setting the ABS excluding only one RRH 30 hasbeen described above, this embodiment is not limited to the example. Forinstance, the ABS setting holding unit 160 may group the eNodeB 10-1 andthe RRHs 30A to 30F into two or more base station groups, and the ABSmay be set excluding some base station groups. Hereafter, it will bedescribed specifically referring to FIG. 10.

FIG. 10 is an explanatory diagram illustrating an example of setting theABS when base stations are grouped. As illustrated in FIG. 10, the ABSsetting holding unit 160 may group the RRHs 30A to 30F into a basestation group including the RRHs 30A to 30C and a base station groupincluding the RRHs 30D to 30F. In this case, the ABS setting holdingunit 160 can cause only the base station group including the RRHs 30A to30C to transmit the CRS in the data region of the subframe #3 by settingthe subframe #3 of the radio frames #M to #N as the ABS for the eNodeB10-1 and the base station group including the RRHs 30D to 30F.

Similarly, as illustrated in the lower part of FIG. 10, the ABS settingholding unit 160 can cause only the base station group including theRRHs 30D to 30F to transmit the CRS in the data region of the subframe#3 by setting the subframe #3 of the radio frames #N+1 to #O as the ABSfor the eNodeB 10-1 and the base station group including the RRHs 30A to30C. As a result, though details will be described later, it is possibleto determine the base station group where the RSRP measurement result inthe UE 20-1 is excellent as a CoMP set.

In addition, the ABS setting holding unit 160 may set the ABS such thatthe base station group where the RSRP measurement result in the UE 20-1is excellent is distinguished first and then the RSRPs of the respectiveRRHs 30 that compose the corresponding base station group can beacquired. According to this configuration, since the RRHs 30 where theRSRP in the UE 20-1 is excellent can be specified in stages, such aconfiguration is effective in terms of the time required and efficiency.

Here, returning to the description about the configuration of the eNodeB10-1 in reference to FIG. 5, the RSRP holding unit 170 holds the RSRPmeasurement results in the UE 20-1 detected by the UL signal detector130 in association with timings (for instance, radio frame numbersand/or subframe numbers) for measurement by the UE 20-1.

FIG. 11 is an explanatory diagram illustrating an example of informationthat is held by the RSRP holding unit 170. When the ABS setting holdingunit 160 sets the ABS, for example, as illustrated in FIG. 8, the RSRPholding unit 170 holds information shown in FIG. 11 on the basis of thefeedback from the UE 20-1. Specifically, the RSRP holding unit 170associates and holds the radio frames #M to #N which are set as the ABSand the RSRPs measured by the UE 20-1 in the corresponding radio framesso that the CRS can be transmitted from only the RRH 30A. Similarly, theRSRP holding unit 170 associates and holds the radio frame numbers towhich the ABS is set and the RSRPs measured by the UE 20-1 in thecorresponding radio frames so that the CRS can be transmitted only fromany one of the RRHs 30.

The CoMP set determining unit 180 determines the CoMP set for performingthe CoMP with each of the UEs 20-1. Specifically, the CoMP setdetermining unit 180 determine which RRH 30 the RSRP in each of theradio frames which are held by the RSRP holding unit 170 is associatedwith by collating the RSRPs with the ABS setting information which isheld by the ABS setting holding unit 160. The CoMP set determining unit180 determines a suitable CoMP set for the UE 20-1 on the basis of theRSRP of each of the RRHs 30.

For instance, the CoMP set determining unit 180 may determine apredetermined number of the RRHs 30 from among ones where the RSRP isexcellent as the CoMP set. Alternatively, the CoMP set determining unit180 may determine the RRHs 30 where the RSRP exceeds a predeterminedvalue as the CoMP set. In addition, the CoMP set determining unit 180may determine the RRHs 30 selected from ones where the RSRP is excellentin a manner that the total value of RSRPs reaches a predetermined valueas the CoMP set. The CoMP set may contain or may not contain eNodeB10-1.

(2-2. Configuration of UE)

Configurations of the eNodeB 10-1 and the RRH 30 according to the firstembodiment have been described hereinabove. Next, the configuration ofthe UE 20-1 according to the first embodiment is described.

FIG. 12 is a functional block diagram illustrating the configuration ofthe UE 20-1 according to the first embodiment. As illustrated in FIG.12, the UE 20-1 includes an antenna group 204, a wireless processingunit 210, a DA/AD converter 220, a DL signal detector 230, a UL signaldetector 240, and an ABS setting position holding unit 250.

The antenna group 204 receives a radio signal from the eNodeB 10-1 andthe RRHs 30 to acquire an electric high frequency signal, and suppliesthe high frequency signal to the wireless processing unit 210. Moreover,the antenna group 204 transmits the radio signal to the eNodeB 10-1 andthe RRHs 30 on the basis of the high frequency signal supplied from thewireless processing unit 210. The UE 20-1 includes the antenna group 204including a plurality of antennas as described above so that the UE 20-1can perform the MIMO communication or the diversity communication.

The wireless processing unit 210 converts the high frequency signalsupplied by the antenna group 204 into a baseband signal (down-linksignal) by performing analog processing such as amplification,filtering, or down conversion. Moreover, the wireless processing unit210 converts the baseband signal (up-link signal) supplied by the DA/ADconverter 220 into the high frequency signal. Thus, the wirelessprocessing unit 210 cooperates with the antenna group 204 so as tofunction as a transmitter and a receiver.

The DA/AD converter 220 converts the down-link signal of the analogformat supplied by the wireless processing unit 210 into the digitalformat, and supplies the converted signal to the DL signal detector 230.Moreover, DA/AD converter 220 converts the up-link signal of the digitalformat supplied by the UL signal generator 240 into the analog format,and supplies the converted signal to the wireless processing unit 210.

The DL signal detector 230 detects a control signal such as PDCCH, userdata such as PDSCH, or the like from the down-link signal supplied bythe DA/AD converter 220. In particular, the DL signal detector 230according to this embodiment extracts information that indicates an ABSsetting position from the PDCCH or the PDSCH. The information thatindicates the ABS setting position corresponds to a location to measurean RSRP and is held in the ABS setting position holding unit 250.Moreover, the DL signal detector 230 functions as a measuring unit thatmeasures the RSRP at the ABS setting position which is held in the ABSsetting position holding unit 250. According to this embodiment, sinceonly some base stations out of the eNodeB 10-1 and the RRHs 30A to 30Ftransmit the CRS at the ABS setting position, the DL signal detector 230can measure the RSRP of only a part of the base stations.

The UL signal generator 240 generates an up-link signal to betransmitted to the eNodeB 10-1 and each of the RRHs 30. Specifically,the UL signal generator 240 generates a control signal like PUCCH and auser data signal like PUSCH. In particular, the UL signal generator 240according to this embodiment generates the PUCCH or the PUSCH includingthe RSRP measurement result obtained by the DL signal detector 230.

(2-3. Operation of Communication System)

Hereinabove, the configurations of the eNodeB 10-1, the RRHs 30, and theUE 20-1 according to the first embodiment have been described. Next, theoperation of a communication system including the eNodeB 10-1, the RRHs30, and the UE 20-1 is described referring to FIG. 13.

FIG. 13 is a flowchart illustrating the operation of the communicationsystem. As illustrated in FIG. 13, when the ABS setting holding unit 160of the eNodeB 10-1 first sets the ABS (S404), the eNodeB 10-1 notifiesthe UE 20-1 of information that indicates the ABS setting position bydedicated signaling (S408). When the information that indicates the ABSsetting position is received, the UE 20-1 transmits a receiptacknowledgement to the eNodeB 10-1 (S412).

Subsequently, the eNodeB 10-1 and the RRHs 30 perform a regularoperation as usual until the ABS setting position arrives (S416, S420).Then, when the ABS setting position arrives, only the RRHs 30 where theABS is not set transmit the CRS in the data region, but neither theeNodeB 10-1 nor the other RRHs 30 transmit the CRS in the data region(S424).

On the other hand, the UE 20-1 measures the RSRP at the ABS settingposition on the basis of the information notified in S408 (S428). Then,the UE 20-1 transmits the RSRP measurement result to the eNodeB 10-1(S432).

After that, the eNodeB 10-1 determines a suitable CoMP set for the UE20-1 on the basis of the RSRP of each of the RRHs 30, or the RSRP ofeach group of the RRHs 30 when the RSRP of each of the RRHs 30 or theRSRP of each group of the RRHs 30 are completely gathered (S436). Then,the eNodeB 10-1 and the RRHs 30 that compose the determined CoMP setperform the CoMP communication with the UE 20-1 (S440). Specifically,the eNodeB 10-1 supplies the down-link signal to the RRHs 30 thatcompose the determined CoMP set, and the RRHs 30 that compose the CoMPset send the supplied down-link signal to the UE 20-1 in cooperationwith the eNodeB 10-1. Further, if the eNodeB 10-1 supplies the down-linksignal to the RRHs 30 that compose the CoMP set as described above, thedown-link signal is transmitted from the corresponding RRHs 30 so thatthe CoMP communication can be achieved. Accordingly, the determined CoMPset is not necessarily notified to the RRHs 30.

As described above, according to the first embodiment, the RSRP in theUE 20-1 of each of the RRHs 30 can be measured even in the situation inwhich each of the RRHs 30 transmits the same CRS. Therefore, the eNodeB10-1 can determine the suitable CoMP set for the UE 20-1 on the basis ofthe RSRP of each of the RRHs 30 in the UE 20-1.

(2-4. Modification)

Although the example where the ABS setting holding unit 160 sets the ABSto different radio frames for different RRHs 30 has been described aboveby referring to FIG. 9 and the like, this embodiment is not limited tothe example. For instance, the ABS setting holding unit 160 may set theABS to a plurality of subframes within the same radio frame fordifferent RRHs 30 as described referring to FIG. 14.

FIG. 14 is an explanatory diagram illustrating a modification of themethod of setting the ABS. As illustrated in FIG. 14, the ABS settingholding unit 160 may set the ABS for the base stations other than theRRH 30A in the subframes #3 of the same radio frame, and set the ABS forthe base stations other than the RRH 30B in the subframe #4. In thiscase, since only the RRH 30A transmits the CRS in the data region of thesubframe #3, the UE 20-1 can measure the RSRP of the RRH 30A in thesubframe #3. Similarly, the UE 20-1 can measure the RSRP of the RRH 30Bin the subframe #4.

In this modification, the UE 20-1 may report the RSRP measurementresults and the subframe numbers where the RSRP is measured, inassociation with each other to the eNodeB 10-1 so that the eNodeB 10-1can distinguish which RRH 30 the RSRP notified by the UE 20-1 isassociated with.

Like this modification, when the ABS is set in different RRHs 30 withrespect to a plurality of subframes of the same radio frame, the time toacquire the RSRPs of the respective RRHs 30 can be shortened.

<3. Second Embodiment>

Hereinabove, the first embodiment of the present disclosure has beendescribed. Next, a second embodiment of the present disclosure isdescribed. The second embodiment acquires an RSRP of each of RRHs 30 bymeasuring a reference signal that is called CSI-RS not by measuring theCRS that is described in the first embodiment. In the following, theCSI-RS is described first, after which details of the second embodimentare described.

(3-1. Regarding CSI-RS)

A channel state information reference signal (CSI-RS) is a referencesignal defined by LTE-Advanced (Rel10). This CSI-RS is used to measure achannel quality, not for the purpose of data demodulation. Therefore,the CSI-RS is thinned out in the directions of frequency and time andinserted comparatively sparsely. For instance, an insertion period ofthe CSI-RS can be set within the range of about 5 ms to 80 ms like 10ms. Since the setting of the CSI-RS (for instance, settings such asadjusting the insertion period to 5 ms or to 10 ms) can be performed foreach UE, it can be said that the setting (configuration) is UE_Specific.

Moreover, as specified in Section 36.2116.10.5.1 of Rel10, apseudo-random sequence is used for the CSI-RS. However, an initial valueof the random sequence is different for each cell (cell ID). Therefore,since the CSI-RS is originally cell_specific, the base station which isa sending station of the CSI-RS can be distinguished by the UE.

However, when the respective RRHs 30 have the same cell ID, the CSI-RSsthat are transmitted by the respective RRHs 30 are also identical.Moreover, although the insertion period of the CSI-RS can be set inunits of a cell, when each of the RRHs 30 has the same cell ID, theCSI-RS insertion periods (timings) of the respective RRHs 30 become alsoidentical. Therefore, it has been difficult to distinguish the RRH 30which is a sending station of the CSI-RS measured by the UE, and todetermine a suitable CoMP set for the UE.

The second embodiment of the present disclosure is a technology that isconceived by taking the above-mentioned circumstances intoconsideration. According to the second embodiment of the presentdisclosure, it is possible to distinguish the RRH 30 which is a sendingstation of the CSI-RS received by the UE. The second embodiment of thepresent disclosure is described in detail below.

(3-2. Configuration of Base Station)

FIG. 15 is a functional block diagram illustrating configurations of aneNodeB 10-2 and RRHs 30 according to the second embodiment of thepresent disclosure. As illustrated in FIG. 15, each of the RRHs 30transmits a down-link signal supplied by the eNodeB 10-2 through anoptical fiber to a UE 20-2 according to the second embodiment similarlyto the first embodiment. Moreover, each of the RRHs 30 supplies anup-link signal received from the UE 20-2 to the eNodeB 10-2 through theoptical fiber. Each of the RRHs 30 has the same cell ID as the eNodeB10-2, and transmits the same cell-specific reference signal (forinstance, CSI-RS).

Moreover, as illustrated in FIG. 15, the eNodeB 10-2 according to thesecond embodiment includes an antenna group 104, a wireless processingunit 110, a DA/AD converter 120, an up-link (UL) signal detector 130, ascheduler 140, and a down-link (DL) signal generator 150, a CSI-RSperiod setting holding unit 162, an RSRP holding unit 172, and a CoMPset determining unit 182. Since the antenna group 104, the wirelessprocessing unit 110, and the DA/AD converter 120 have been described inthe first embodiment, detailed description thereof will not be givenhere.

The UL signal detector 130 detects a control signal such as PUCCH anduser data such as PUSCH from the up-link signal supplied by the DA/ADconverter 120. In particular, the UL signal detector 130 according tothis embodiment detects an RSRP measurement result obtained through aCSI-RS measurement in the UE 20-2 from the up-link signal supplied bythe DA/AD converter 120. The RSRP measurement result may be contained inthe PUSCH.

The scheduler 140 schedules resources to be used by the eNodeB 10-2,each of the RRHs 30, and the UE 20-2 for communication. In particular,the scheduler 140 according to this embodiment performs schedulingaccording to the CSI-RS insertion period set by the CSI-RS periodsetting holding unit 162. Moreover, the scheduler 140 schedules thecommunication with the UE 20-2 by using the CoMP set, which isdetermined for the communication with the UE 20-2 by the CoMP setdetermining unit 180.

The DL signal generator 150 generates the down-link signal to betransmitted from the eNodeB 10-2 and each of the RRHs 30. Specifically,the DL signal generator 150 generates PDCCH, PDSCH, and the likeaccording to the scheduling performed by the scheduler 140. In addition,the DL signal generator 150 according to this embodiment inserts aCSI-RS into the eNodeB 10-2 and each of the RRHs 30 according to theperiod set by the CSI-RS period setting holding unit 162. In addition,the PDCCH or the PDSCH may contain information about the CSI-RSinsertion period set by the CSI-RS period setting holding unit 162.

The CSI-RS period setting holding unit 162 sets the CSI-RS insertionperiod for the eNodeB 10-2 and each of the RRHs 30. For instance, theCSI-RS period setting holding unit 162 sets different insertion periods(insertion timings) for the eNodeB 10-2 and each of the RRHs 30. As aresult, it is possible to specify a sending station of the CSI-RS whenthe UE 20-2 receives the CSI-RS at a certain timing. Hereafter, theCSI-RS insertion period is described more specifically referring to FIG.16.

FIG. 16 is an explanatory diagram illustrating a concrete example of theCSI-RS insertion period. As illustrated in FIG. 16, the CSI-RS periodsetting holding unit 162 sets the CSI-RS insertion periods such thatthere may be timings at which only some base stations out of the eNodeB10-2 and each of the RRHs 30 transmit the CSI-RS.

For instance, the CSI-RS period setting holding unit 162 sets the CSI-RSinsertion periods named t1, t3, t5, and t7 for the eNodeB 10-2 asillustrated in FIG. 16, and sets the CSI-RS insertion periods named t2and t4 for the RRH 30A. Therefore, only the RRH 30A transmits the CSI-RSfor t2 and t4. Similarly, the CSI-RS period setting holding unit 162sets the CSI-RS insertion periods named t6 and t8 for the RRH 30B.Therefore, only the RRH 30B transmits the CSI-RS for t6 and t8.Similarly, it is possible to generate timings at which only each of theRRHs 30 transmits the CSI-RS by setting CSI-RS insertion periodsdifferent from those of the eNodeB 10-2 for each of the RRHs 30.

The example of setting the CSI-RS insertion periods named t1, t3, t5,and t7 only for the eNodeB 10-2 is shown in FIG. 16, but these CSI-RSinsertion periods may be set for each of the RRHs 30. In such a case,the UEs up to Rel10 receive the CSI-RSs from the plurality of RRHs 30for the same periods named t1, t3, t5, and t7 and acquire channelswithout distinguishing sending stations of the respective CSI-RSs. Onthe other hand, the UE 20-2 down from Rel11 can receive the CSI-RSs atthe timings at which only each of the RRHs 30 transmits by setting aplurality of periods as the CSI-RS reception periods. That is, themethod of setting the CSI-RS according to the second embodiment canensure compatibility with existing UEs.

Moreover, though the example of setting different CSI-RS insertionperiods for each of the RRHs 30 has been described in theabove-mentioned embodiment, this embodiment is not limited to theexample. For instance, the CSI-RS period setting holding unit 162 maygroup the RRHs 30A to 30F into two or more groups, and set the sameSCI-RS insertion period for the RRHs 30 that compose the same group.Hereinbelow, such a setting is described in detail referring to FIG. 17.

FIG. 17 is an explanatory diagram illustrating an example of settingCSI-RS insertion periods when the RRHs 30 are grouped. As illustrated inFIG. 17, the CST-RS period setting holding unit 162 may group the RRHs30A to 30F into a group including the RRHs 30A to 30C and a groupincluding the RRHs 30D TO 30F. In this case, the CSI-RS period settingholding unit 162 can cause only the RRHs 30A to 30C to transmit theCSI-RS for t2 and t4 by setting the CSI-RS insertion periods named t2and t4 for the group including the RRHs 30A to 30C.

Similarly, the CSI-RS period setting holding unit 162 can cause only theRRHs 30D to 30F to transmit the CSI-RS for t6 and t8 by setting theCSI-RS insertion periods named t6 and t8 for the group including theRRHs 30D to 30F. As a result, it is possible to determine the groupwhere the RSRP measurement result in the UE 20-2 is excellent, forinstance, as a CoMP set.

In addition, the CSI-RS period setting holding unit 162 may set theCSI-RS insertion periods such that the group where the RSRP measurementresult in the UE 20-2 is excellent is distinguished first and then theRSRP of each of the RRHs 30 that compose the corresponding group can beachieved. According to this configuration, since the RRHs 30 where theRSRP in the UE 20-2 is excellent can be specified in stages, theconfiguration is effective in terms of the time required and efficiency.

Here, returning to the description about the configuration of the eNodeB10-2 in reference to FIG. 15, the RSRP holding unit 172 holds the RSRPmeasurement results in the UE 20-2 detected by the UL signal detector130 in association with timings (for instance, radio frame numbers andsubframe numbers) for measurement by the UE 20-2.

The CoMP set determining unit 182 determines the CoMP set for performingthe CoMP with each of the UEs 20-2. Specifically, the CoMP setdetermining unit 182 determines which RRH 30 the RSRP in each of theradio frames held in the RSRP holding unit 172 is associated with bycollating the RSRP with setting information of each base station held inthe CSI-RS period setting holding unit 162. The CoMP set determiningunit 182 determines a suitable CoMP set for the UE 20-2 on the basis ofthe RSRP of each of the RRHs 30.

For instance, the CoMP set determining unit 182 may determine apredetermined number of the RRHs 30 from among ones where the RSRP isexcellent as the CoMP set. Alternatively, the CoMP set determining unit182 may determine the RRHs 30 where the RSRP exceeds a predeterminedvalue as the CoMP set. In addition, the CoMP set determining unit 182may determine, as the CoMP set, the RRHs 30 selected from among oneswhere the RSRP is excellent such that the total value of the RSRPsreaches a predetermined value. The CoMP set may contain or may notcontain eNodeB 10-2.

(3-3. Configuration of UE)

Hereinabove, the configurations of the eNodeB 10-2 and the RRHs 30according to the second embodiment have been described. Next, theconfiguration of the UE 20-2 according to the second embodiment isdescribed.

FIG. 18 is a functional block diagram illustrating the configuration ofthe UE 20-2 according to the second embodiment. As illustrated in FIG.18, the UE 20-2 includes an antenna group 204, a wireless processingunit 210, a DA/AD converter 220, a DL signal detector 230, a UL signaldetector 240, and a CSI-RS period holding unit 252. Since the antennagroup 204, the wireless processing unit 210, and the DA/AD converter 220have been described in the first embodiment, a detailed descriptionthereof is not given below.

The DL signal detector 230 detects a control signal like PDCCH and userdata like PDSCH from a down-link signal supplied by the DA/AD converter220. In particular, the DL signal detector 230 according to thisembodiment extracts information that indicates the CSI-RS insertionperiod from the PDCCH or the PDSCH. The information that indicates theCSI-RS insertion period corresponds to a location for RSRP measurementand is held in the CSI-RS period holding unit 252. Moreover, the DLsignal detector 230 measures the RSRP for the CST-RS insertion periodheld in the CSI-RS period holding unit 252. According to thisembodiment, since only some base stations of the eNodeB 10-2 and theRRHs 30A to 30F transmit the CSI-RSs for the CSI-RS insertion periods,the DL signal detector 230 can measure the RSRPs of a part of the basestations.

The UL signal generator 240 generates an up-link signal to betransmitted to the eNodeB 10-2 and each of the RRHs 30. Specifically,the UL signal generator 240 generates a control signal like PUCCH and auser data signal like PUSCH. In particular, the UL signal generator 240according to this embodiment generates the PUCCH or the PUSCH includingthe RSRP measurement result obtained by the DL signal detector 230.

(3-4. Operation of Communication System)

Hereinabove, the operations of the eNodeB 10-2, the RRHs 30, and the UE20-2 according to the second embodiment have been described. Next, theoperation of a communication system including the eNodeB 10-2, the RRHs30, and the UE 20-2 is described referring to FIG. 19.

FIG. 19 is a flowchart illustrating the operation of the communicationsystem. As illustrated in FIG. 19, when the CSI-RS period settingholding unit 162 of the eNodeB 10-2 first sets a CSI-RS insertion periodfor each of the RRHs 30 (S504), the eNodeB 10-2 notifies the UE 20-2 ofinformation that indicates a CSI-RS insertion period by dedicatedsignaling (S508). When the information that indicates the CSI-RSinsertion period is received, the UE 20-2 transmits a receiptacknowledgement to the eNodeB 10-2 (S512).

After that, the eNodeB 10-2 and the RRHs 30 perform a regular operationas usual until the CSI-RS insertion period arrives (S516, 5420). Whenthe CSI-RS insertion period arrives, the CSI-RS is transmitted only fromthe RRH 30 for which the coming insertion period is set (S524).

On the other hand, the UE 20-2 measures the RSRP for the CSI-RSinsertion period on the basis of the information notified in 5508(S528). Then, the UE 20-2 transmits the RSRP measurement result to theeNodeB 10-2 (S532).

After that, the eNodeB 10-2 determines a suitable CoMP set for the UE20-2 on the basis of the RSRP of each of the RRHs 30 or the RSRP of eachgroup of the RRHs 30 when the RSRP of each of the RRHs 30 or the RSRP ofeach group of the RRHs 30 are completely gathered (S536). The eNodeB10-2 and the RRHs 30 that compose the determined CoMP set perform theCoMP communication with the UE 20-2 (S540). Specifically, the eNodeB10-2 supplies the down-link signal to the RRH 30 that composes thedetermined CoMP set, and the RRH 30 that composes the CoMP set transmitsthe supplied down-link signal to the UE 20-2 in cooperation with theeNodeB 10-2. In addition, if the eNodeB 10-2 supplies the down-linksignal to the RRH 30 which composes the CoMP set as stated above, thedown-link signal is transmitted from the corresponding RRH 30 so thatthe CoMP communication can be achieved. Accordingly, the determined CoMPset is not necessarily notified to the RRH 30.

As described above, according to the second embodiment of the presentdisclosure, the RSRP can be measured in the UE 20-2 of each of the RRHs30 even in the situation in which each of the RRHs 30 transmits the sameCSI-RS. Therefore, the eNodeB 10-2 can determine the COMP set that issuitable for the UE 20-2 on the basis of the RSRP of each of the RRHs 30in the UE 20-2.

(3-5. First Modification)

Although the example where the CSI-RS period setting holding unit 162sets the CSI-RS insertion period for different RRHs 30 in different timeframes has been described referring to FIG. 16, but this embodiment isnot limited to the example. For instance, the CSI-RS period settingholding unit 162 may set different CSI-RS insertion periods fordifferent RRHs 30 in the time frame that overlaps as illustrated in FIG.20.

In this case, the UE 20-2 may report RSRP measurement results and RSRPmeasuring periods in association with each other to the eNodeB 10-2 sothat the eNodeB 10-2 can distinguish which RRHs 30 the RSRP reportedfrom the UE 20-2 is associated with.

Like the first modification, the time to acquire the RSRP of each of theRRHs 30 can be shortened by setting different CSI-RS insertion periodsfor different RRHs 30 in the overlapping time frame.

(3-6. Second Modification)

By the way, the technology called CSI-RS Muting is standardized in Rel10considering the fact that the reception of CSI-RS of the adjacent cellis disturbed by PDSCH or the like of high power from a serving basestation. Muting is the technology which stops the transmission from theserving base station by using the resource block corresponding to theposition from which the C SI-RS of the adjacent cell is transmitted.Actually, it is considered that the transmission of the PDSCH is stoppednot only at the position from which the CSI-RS of the adjacent theory istransmitted but also at around the transmission position. In short, theCSI-RS muting is a technology which protects the CSI-RS of the adjacentcell from interference by the PDSCH of the serving base station.

Therefore, according to the second modification, the RRH 30 which is asending station of the CSI-RS received by the UE 20-2 can bedistinguished by using a method named CSI-RS+Enhanced_Muting thatimproves the CSI-RS muting like the second embodiment.

Specifically, the eNodeB 10-2 mutes the CSI-RSs from the RRHs 30 excepta part of the RRHs 30 in the situation in which the CSI-RS insertionperiods of the eNodeB 10-2 and each of the RRHs 30 are identical. As aresult, since only some RRHs 30 of a plurality of RRHs transmit theCST-RS, the RRH 30 which is the sending station of the CSI-RS receivedby the UE 20-2 can be distinguished. Hereafter, such an operation willbe described in detail referring to FIG. 21.

FIG. 21 is an explanatory diagram illustrating CSI-RS+Enhanced_Mutingaccording to the second modification. As illustrated in FIG. 21, theCSI-RSs from the RRHs 30 other than the RRH 30A is muted for a periodP1. Therefore, the RRH 30A can be specified as the sending station ofthe CSI-RS received by the UE 20-2 for the period P1.

Moreover, since the CSI-RSs from the RRHs 30 other than the RRH 30B aremuted for a period P2, the RRH 30B can be specified as the sendingstation of the CSI-RS received by the UE 20-2 for the period P2.Moreover, since the CSI-RSs from the RRHs 30 other than the RRH 30C aremuted for a period P3, the RRH 30C can be specified as the sendingstation of the CSI-RS received by the UE 20-2 for the period P3.

In Modification 2, the eNodeB 10-2 notifies the UE 20-2 of the period ofa single CSI-RS beforehand, and the UE 20-2 may measure the RSRP forthis CSI-RS period and report the measurement result to the eNodeB 10-2.As a result, the eNodeB 10-2 can determine a suitable CoMP set for theUE 20-2 on the basis of the RSRP measurement result reported from the UE20-2.

<4. Conclusion>

As described above, according to the embodiments of the presentdisclosure, the RSRP can be measured in the UE 20 of each of the RRHs 30even in the situation in which each of the RRHs 30 operates based on thesame cell ID. Therefore, the eNodeB 10 can determine the CoMP set thatis suitable for the UE 20 on the basis of the RSRP of each of the RRHs30 in the UE 20. As a result, it is possible to achieve an improvementof system throughput and a reduction in power consumption because thetransmission from the RRHs 30 that do not really contribute to theimprovement of the reception quality of the UE 20 can be avoided.

Although the preferred embodiments of the present disclosure have beendescribed in detail referring to the accompanying drawings, thetechnical scope of the present disclosure is not limited to theexamples. It is understood that those ordinarily skilled in thetechnical field of the present disclosure may certainly conceive variousalterations or modifications within the scope of the technical spiritdescribed in the claims, and be aware that these naturally fall withinthe technical scope of the present disclosure.

For instance, although the examples of determining the CoMP set on thebasis of the measurement result of the RSRP as a reference signal whichis measured by the UE 20 have been described above, the technical scopeof the present disclosure is not limited to the examples. As amodification, the UE 20 may feedback an index that indicates a receptionquality such as an error occurrence rate of a signal sent from each ofthe RRHs 30 to the eNodeB 10, and the eNodeB 10 may determine the CoMPset on the basis of the index.

Moreover, each step in the processing performed by the eNodeB 10 and theUE 20 of this specification is not necessarily processed in a timeseries manner along the order described in the sequence diagram. Forinstance, each step in the processing of the eNodeB 10 and the UE 20 maybe processed in order different from the order described in the sequencediagram or may be processed in parallel.

Furthermore, the second modification of the second embodiment has beendescribed by using an example in which the RSRPs corresponding to therespective combinations of the RRHs 30 are acquired by using CSI-RSMuting, but the signals used are not limited to the CST-RS. For example,a mechanism similar to the above-described mechanism can be provided bypreparing an RS other than the CSI-RS, or a new RS. Especially when aplurality of RRHs 30 (or a plurality of eNodeBs 10) sends the RS usingthe same resource element, the RSRPs corresponding to the respectivecombinations can be obtained using the same mechanism as the presenttechnology.

Furthermore, though the CoMP set is determined by using an estimation ofa desired signal and an estimation of an interference signal, the methodof acquiring these estimations has not been sufficiently studied yet.Moreover, the estimation of the interference amount in CoMP environmentcan be used not only for the determination of the CoMP set but also asinformation for controlling other interferences, such as ICIC(Inter-Cell Interference Coordination) of the LTE Release 8.Accordingly, the estimation of the interference amount from each eNodeBalso becomes important.

That is, the technology of the present disclosure is used not only forthe purpose of acquiring a desired RSRP, but also for the purpose ofacquiring an intensity of an interference component. That is, accordingto the technology of the present disclosure, the interference componentfrom the base stations such as the RRHs 30 or the eNodeBs 10 that havethe same cell ID can be acquired for each of different combinations ofthe base stations. This is implemented, for example, in a way that theUL signal detector 130 of the eNodeB 10 acquires a detection result ofthe interference component which is obtained from the uplink signalthrough RS measurement in the UE 20, and the RSRP holding unit 170stores the detection result of the interference component. A specificmethod of acquiring the interference component in each of the UEs 20 isas follows: for example, a correlation with a reception signal isobtained by using an RS (Reference Signal) of each of the eNodeBs 10 asa known signal, and the interference amount of each eNodeB 10 can beacquired by using the magnitude of the correlation. It can be said thatthe method of acquiring the magnitude of this interference component andthe method of acquiring the magnitude of the desired component among thereception signals are the same.

Moreover, it is possible to produce a computer program which causeshardware embedded in the eNodeB 10 and the UE 20, such as a CPU, a ROM,and a RAM to perform the same functions as those of the respectivecomponents of the eNodeB 10 and the UE 20 that have been describedabove. Moreover, a storage medium which stores the computer program isprovided.

Moreover, the following configurations also belong to the technicalscope of the present disclosure.

According to a communication device embodiment, the device includes

a receiver that receives information indicating a timing at which apredetermined signal is transmitted from a transmitting base station ofa plurality of base stations having a same cell ID, wherein

said receiver determines that said predetermined signal has beentransmitted from the transmitting base station based on the timingobserved by said receiver.

According to one aspect of the embodiment, the communication devicefurther includes

a transmitter that transmits an indication of measurement results madeby said receiver of said predetermined signal so that a subset of saidplurality of base stations are assigned for future communications withsaid communication device based on said measurement results.

According to another aspect

the receiver is configured to receive the predetermined signal from thesubset of said plurality of base stations in a data portion of apredetermined subframe, and

other base stations of said plurality of base stations not transmittingsaid predetermined signal in said predetermined subframe so that thereceiver can distinguish whether the predetermined signal is from one ofthe subset of said plurality of base stations or from the other basestations.

According to another aspect

the predetermined subframe is an almost blank subframe that includes thepredetermined signal.

According to another aspect

the predetermined subframe is located in different respective time slotsfor different base stations of the plurality of base stations.

According to another aspect

the receiver is configured to measure a received signal power of saidpredetermined signal for each of the plurality of base stations.

According to another aspect

said transmitter is configured to transmit an indication of saidreceived signal power to the transmitting base stations for assisting insetting the subset of said plurality of base stations.

According to another aspect

the receiver determines an interference component as part of saidmeasurement result.

According to another communication device embodiment, the deviceincludes

a communication controlling device that includes a setting unit thatsets a timing at which a predetermined signal is transmitted only fromsome base stations of a plurality of base stations having a same cell IDso a user equipment can determine that the predetermined signal has beentransmitted from a transmitting base station based on a receive timingobserved by the user equipment.

According to one aspect of the embodiment, the device further includes

a wireless processing unit that receives a measurement result from auser equipment of said predetermined signal as received at said userequipment and assigns a subset of said plurality of base stations havinga same cell ID to provide future communications with user equipment.

According to another aspect

the communication controlling device sets a format of said predeterminedsignal to be included in a predetermined subframe transmitted from thesubset of said plurality of base stations having a same cell ID.

According to another aspect

the communication controlling device positions said predeterminedsubframe as an almost blank subframe that includes the predeterminedsignal.

According to another aspect

the predetermined subframe is located in different respective time slotsfor different base stations of the plurality of base stations.

According to another aspect

the wireless processing unit receives a signal from the user equipmentthat includes a measure of a received signal power at said userequipment of said predetermined signal transmitted from respective ofthe plurality of base stations.

According to another aspect

said wireless processing unit receives an indication of said receivedsignal power for assisting the communications controlling device insetting the subset of said plurality of base stations in associationwith a subframe number of said predetermined signal.

According to another aspect

the wireless processing unit receives an interference component as partof said measurement result.

According to a method embodiment, the method includes

receiving wirelessly at a user equipment receiver information indicatinga timing at which a predetermined signal is transmitted from atransmitting base station of a plurality of base stations having a samecell ID; and

determining that said predetermined signal has been transmitted from thetransmitting base station based on the timing observed by said userequipment receiver.

According to one aspect of the embodiment, the method further includes

transmitting an indication of measurement results made by said receiverof said predetermined signal so that a subset of said plurality of basestations are assigned for future communications with said communicationdevice based on said measurement results.

According to another aspect

the receiving includes receiving the predetermined signal from thesubset of said plurality of base stations in a data portion of apredetermined subframe, and

other base stations of said plurality of base stations not transmittingsaid predetermined signal in said predetermined subframe so that thereceiver can distinguish whether the predetermined signal is from one ofthe subset of said plurality of base stations or from the other basestations.

According to another aspect

the predetermined subframe is an almost blank subframe that includes thepredetermined signal.

According to another aspect

the predetermined subframe is located in different respective time slotsfor different base stations of the plurality of base stations.

According to another aspect

the receiving includes measuring a received signal power of saidpredetermined signal for each of the plurality of base stations.

According to another aspect

said transmitting includes transmitting an indication of said receivedsignal power to the transmitting base stations for assisting in settingthe subset of said plurality of base stations.

According to another aspect

said receiving includes determining an interference component as part ofsaid measurement result.

According to another method embodiment, the method includes

setting a timing at which a predetermined signal is transmitted onlyfrom some base stations of a plurality of base stations having a samecell ID; and

transmitting said predetermined signal to a user equipment so the userequipment can determine that the predetermined signal has beentransmitted from a transmitting base station based on a receive timingobserved by the user equipment.

According to one aspect, the method further includes

receiving a measurement result from a user equipment of saidpredetermined signal as received at said user equipment and assigning asubset of said plurality of base stations having a same cell ID toprovide future communications with user equipment based on saidmeasurement result.

According to another aspect

setting a format of said predetermined signal to be included in apredetermined subframe transmitted from the subset of said plurality ofbase stations having a same cell ID.

According to another aspect

said setting includes setting said predetermined subframe as an almostblank subframe that includes the predetermined signal.

According to another aspect

the predetermined subframe is located in different respective time slotsfor different base stations of the plurality of base stations.

According to another aspect, the method further includes

receiving a signal from the user equipment that includes a measure of areceived signal power of said predetermined signal from the plurality ofbase stations at said user equipment.

According to another aspect

said receiving includes receiving an indication of said received signalpower for assisting in setting the subset of said plurality of basestations in association with a subframe number of said predeterminedsignal.

According to another aspect

the receiving includes receiving an interference component as part ofsaid measurement result.

REFERENCE SIGNS LIST

-   10, 10-1, 10-2 eNodeB-   12 Core network-   20, 20-1, 20-2 UE-   30 RRH-   104, 204, 304 Antenna group-   110, 210, 310 Wireless processing unit-   120, 220 DA/AD converter-   130 UL signal detector-   140 Scheduler-   150 DL signal generator-   160 ABS setting holding unit-   162 CSI-RS period setting holding unit-   170, 172 RSRP holding unit-   180, 182 CoMP set determining unit-   230 DL signal detector-   240 UL signal generator-   250 ABS setting position holding unit-   252 CSI-RS period holding unit

1. An electronic device comprising: wireless processing circuitrycoupled to at least one antenna and configured to: communicate with aplurality of base stations, the base stations including at least a firstbase station and a second base station; receive configurationinformation indicating one or more Channel State Information-ReferenceSignal (CSI-RS) insertion periods; and a signal detector includingcircuitry configured to measure receiving power in accordance with theconfiguration information, wherein the first base station and the secondbase station have an identical cell ID, and the first base station andthe second base station are distinguishable from each other based on aplurality of first CSI-RSs transmitted by the first base station, aplurality of second CSI-RSs muted by the first base station, a pluralityof third CSI-RSs transmitted by the second base station, and a pluralityof fourth CSI-RSs muted by the second base station, and wherein theconfiguration information indicates at least a first period of the firstCSI-RSs, a second period of the second CSI-RSs, a third period of thethird CSI-RSs, and a fourth period of the fourth CSI-RSs.
 2. Theelectronic device of claim 1, wherein the configuration informationfurther indicates a plurality of CSI-RS insertion periods correspondingto a plurality of base stations.
 3. The electronic device of claim 1,wherein the wireless processing circuitry is further configured tocommunicate with the plurality of base stations by Coordinated MultiplePoint transmission and reception (CoMP).
 4. The electronic device ofclaim 1, wherein one of the plurality of first CSI-RSs is receivedduring a timing when one of the plurality of second CSI-RSs is muted. 5.The electronic device of claim 1, wherein the receiving power ismeasured during a plurality of timings, wherein the first base stationis configured to transmit the first CSI-RSs and mute the second CSI-RSsduring the plurality of timings, wherein the second base station isconfigured to transmit the third CSI-RSs and mute the fourth CSI-RSsduring the plurality of timings, and wherein each of the plurality oftimings are temporally spaced at equal intervals.
 6. A wirelesscommunication method comprising: communicating with a plurality of basestations, the base stations including at least a first base station anda second base station; receiving configuration information indicatingone or more Channel State Information-Reference Signal (CSI-RS)insertion periods; and measuring receiving power in accordance with theconfiguration information, wherein the first base station and the secondbase station have an identical cell ID, and the first base station andthe second base station are distinguishable from each other based on aplurality of first CSI-RSs transmitted by the first base station, aplurality of second CSI-RSs muted by the first base station, a pluralityof third CSI-RSs transmitted by the second base station, and a pluralityof fourth CSI-RSs muted by the second base station, and wherein theconfiguration information indicates at least a first period of the firstCSI-RSs, a second period of the second CSI-RSs, a third period of thethird CSI-RSs, and a fourth period of the fourth CSI-RSs.
 7. Anelectronic device comprising: wireless processing circuitry coupled toat least one antenna and configured to: communicate with a terminaldevice that is configured to communicate with a plurality of basestations including a first base station and a second base station; andtransmit configuration information to the terminal device, theconfiguration information indicating one or more Channel StateInformation-Reference Signal (CSI-RS) insertion periods, wherein theterminal device is configured to measure receiving power in accordancewith the configuration information, wherein the first base station andthe second base station have an identical cell ID, and the first basestation and the second base station are distinguishable from each otherbased on a plurality of first CSI-RSs transmitted by the first basestation, a plurality of second CSI-RSs muted by the first base station,a plurality of third CSI-RSs transmitted by the second base station, anda plurality of fourth CSI-RSs muted by the second base station, andwherein the configuration information indicates at least a first periodof the first CSI-RSs, a second period of the second CSI-RSs, a thirdperiod of the third CSI-RSs, and a fourth period of the fourth CSI-RSs.8. The electronic device of claim 7, wherein the configurationinformation further indicates a plurality of CST-RS insertion periodscorresponding to a plurality of base stations.
 9. The electronic deviceof claim 7, wherein the wireless processing circuitry is furtherconfigured to communicate with the terminal device by CoordinatedMultiple Point transmission and reception (CoMP).